Method for drawing metallic tube

ABSTRACT

In a method for drawing a tube blank while supplying lubricant to an inner surface of the tube blank from a discharge opening of a rod, the lubricant is adhered appropriately to the inner surface both in the circumferential direction of the tube blank and in the longitudinal direction thereof without using any application member such as a core. While drawing a metal tube blank  2  by passing between a die  10  for shaping an outer surface and a plug  11  for shaping an inner surface, the lubricant L is discharged intermittently from a discharge opening  21  provided in an outer peripheral surface of a rod  20  supporting the plug  11  toward an upper region  40  of the tube blank  2  positioned higher than the center of the tube  2  in the up-and-down direction to thereby make the lubricant adhere to a portion of the inner surface of the tube  2  including the highest position P 1  of the inner surface of the tube  2.

TECHNICAL FIELD

The present invention relates to a method for drawing a metal tube capable of producing a metal drawn tube excellent in dimensional accuracy, which can be preferably used as an OPC photoconductive drum substrate for electro-photographic apparatuses, such as, e.g., copying machines, laser beam printers, and facsimile apparatuses, and also relates to an apparatus for carrying out the drawing method. In the description of this specification, the wording of “rear/rearward” used with reference to a drawing apparatus and a drawing method denotes a direction toward a tube blank or a raw tube with respect to a drawn tube, and “front/forward” denotes a direction toward a drawn tube with respect to the tube blank.

BACKGROUND TECHNIQUE

In recent years, as an OPC photoconductive drum substrate for electro-photographic apparatuses, such as, e.g., copying machines, laser beam printers, or facsimile machines, a non-cut tube suitable for mass production has been widely used. One of such non-cut tubes is a so-called ED tube obtained by drawing an aluminum extruded tube blank, which is suitable for mass production in that a plurality of product tubes can be manufactured by a single drawing process. The production method is now getting an attention as a production method which complies with mass consumption accompanied by market expansion.

Such an ED tube is produced by initially obtaining an aluminum extruded tube blank by extruding an aluminum billet, and then cutting the extruded tube blank into a predetermined length. Thereafter, the cut tube is subjected to one pass or two or more passes of drawing processing using a die and a plug to obtain an aluminum tube having a predetermined configuration (i.e., predetermined outer diameter, inner diameter, wall thickness), and further subjected to a cutting process, a chamfering process for chamfering end portions, a washing process, and an inspection process for inspecting dimensions and appearance to thereby obtain an ED tube.

In such a drawing process for an aluminum tube used as a photoconductive drum substrate, supplying lubricant to an outer surface of a tube can be easily performed by previously applying lubricant on the outer surface or supplying lubricant so as to flow down on the outer surface during the drawing process. However, when supplying lubricant to an inner surface of a tube, especially in the case of an ED tube in which a tube blank is subjected to two or more passes of continuous drawing processing at a high speed, it was difficult to previously supply lubricant to an inner surface of a tube. For this reason, there was no choice but to perform drawing processing in a state in which a plug with lubricant applied thereon is inserted in a tube. In contrast to an outer surface of a tube to which lubricant can be supplied as needed, in the case of supplying lubricant to an inner surface of a tube, lubricant may sometimes become insufficient during the drawing processing, resulting in burning of the inner surface, which deteriorates the run-out accuracy of the drawn tube.

To cope with such a problem, the present applicant has proposed a drawing apparatus capable of supplying lubricant to an inner surface of a tube blank as needed in which openings are formed in a peripheral wall of a hollow rod supporting a plug to discharge the lubricant supplied to the inner space of the hollow rod from the rear end portion thereof. In such a drawing apparatus, in order to evenly spread the lubricant adhered to the inner surface of the tube blank, a core is attached to the rod (see Patent Documents 1 and 2).

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Unexamined Laid-open Japanese Patent Application     Publication No. 2009-22982 (JP-A-2009-22982) -   Patent Document 2: Unexamined Laid-open Japanese Patent Application     Publication No. 2009-45663 (JP-A-2009-45663)

SUMMARY OF THE INVENTION Problems to be Solved by The Invention

In the aforementioned drawing apparatus, the drawing is performed while discharging a predetermined amount of lubricant. However, the discharge amount of lubricant is kept constant, and after completion of a drawing process of a single extruded tube blank, the drawn tube is taken out from the apparatus while suspending the supply of lubricant, and then a subsequent extruded tube blank is set to the apparatus and supply of lubricant is resumed at the time of initiating the subsequent drawing process. According to such a step in which lubricant is supplied discontinuously, suspending the supply of lubricant causes outflow of the lubricant accumulated in the rod through the openings. Furthermore, since the inner space of the rod is not filled with lubricant, even if the supply of lubricant is resumed, it takes a time until a certain amount of lubricant starts discharging from the openings formed in the vicinity of the plug, resulting in poor responsiveness of lubricant discharge. For this reason, if a drawing process is initiated in a state in which lubricant is not sufficiently discharged, burning may occur at the drawing initiation portion. If a drawing process is performed after waiting for the recovery of discharge amount of lubricant, the processing efficiency deteriorates.

Furthermore, when the core in contact with the tube blank is abraded, the lubricant cannot be evenly applied, which necessitates changing of cores as consumable supplies.

Also, in a method in which lubricant is directly discharged to an inner surface of a tube blank from discharge openings of a rod without using a core, the amount of lubricant used must be increased to prevent possible shortage of lubricant. As a result, in addition to the increase in consumption of lubricant, the burden of cleansing at the following step increases since the amount of lubricant carried out together with the drawn tube increases.

Problems to be Solved by the Invention

In view of the aforementioned technical background, in a drawing method in which drawing is performed while supplying lubricant to an inner surface of a tube blank through a discharge opening of a rod, the present invention aims to make an appropriate amount of lubricant adhere to the tube blank both in a circumference direction of the tube blank and in the longitudinal direction thereof without using an application member such as a core.

In a drawing process using a drawing die and a plug, it is required that a contact surface between a metal tube blank and a plug be filled with a required amount of lubricant. To decrease the excessive amount of lubricant, it is preferred to supply a required amount of lubricant from a position in the vicinity of the contact surface between the metal tube blank and the plug. However, in the case of supplying lubricant from a position in the vicinity of the contact surface between the metal tube blank and the plug, there are problems such that (1) a gap for disposing a lubricant supplying structure is required, (2) a thickness of lubricant becomes uneven on the contact surface between the metal tube blank and the plug, and (3) an excessive amount of lubricant, which is a safer amount of lubricant, should be applied to avoid possible burning since an insufficient amount of lubricant may cause occurrence of burning.

(1) The problem that a gap for disposing a lubricant supplying mechanism is required:

A position which is close to the contact surface between a metal tube blank and a plug is small in gap, and therefore it is difficult to place a lubrication supplying mechanism. For this reason, in the present invention, a lubricant supplying mechanism is provided at a rod having a larger gap between the rod and the metal tube blank.

(2) The problem that a thickness of lubricant becomes uneven on a contact surface between a metal tube blank and a plug:

If the lubricant supplying mechanism is not high in accuracy of supplying lubricant, a thickness of the lubricant adhered to a contact surface between the metal tube blank and the plug becomes uneven in the circumferential direction of the contact surface. A lubricant supplying mechanism high in accuracy of supplying lubricant is complex in structure and expensive. In the present invention, lubricant is discharged toward an upper region of an inner surface of a tube blank higher than a central position of the tube blank in the up-and-down direction or in the vertical direction through a discharge opening formed in a portion of a rod positioned rearward of the contact surface between the metal tube blank and the plug with respect to the drawing direction, so that the excess amount of lubricant applied to the portion including the highest position of the inner surface of the tube blank flows down under its own weight. The lubricant remained on the inner surface of the tube blank after flowing down of an excess amount of lubricant has an even thickness required for drawing. Because it takes time for the excessive amount of lubricant to flown down under its own weight, the discharge opening is formed, not in a position of the rod close to the contact surface between the metal tube blank and the plug, but in a position of the rod away from the contact surface between the metal tube blank and the plug. It is preferable that the discharge opening is provided at a position 10 mm or more away from the contact surface between the metal tube blank and the plug.

(3) The problem that an excessive amount of lubricant, which is a safer amount of lubricant, should be applied to prevent possible burning since insufficient amount of lubricant may cause burning.

To prevent occurrence of burning, it was required to provide more than an amount of lubricant which fills up the gap between the tube blank and the plug, and therefore, in a conventional technology, lubricant was continuously supplied to provide so that an excessive amount of lubricant always exists.

In the present invention, lubricant is discharged intermittently or discontinuously to intentionally create a region in which no lubricant is adhered to an inner surface of the tube blank before reaching the plug, so that the excessive lubricant is used (consumed) in “the region in which no lubricant is adhered.”

The present invention has the structure as recited in the following Items [1] to [7].

[1] A method for drawing a metal tube blank,

while drawing the metal tube blank between a die for shaping an outer surface of the tube blank and a plug for shaping an inner surface of the tube blank, intermittently discharging lubricant through a discharge opening formed in a rod supporting the plug toward an upper region of the tube blank positioned higher than a center of the tube blank in an up-and-down direction to apply the lubricant to a portion of the inner surface of the tube blank including the highest position of the inner surface of the tube blank.

[2] The method for drawing a metal tube blank as recited in Item 1, wherein the lubricant is discharged intermittently in a manner such that a discharge amount of the lubricant is gradually increased.

[3] The method for drawing a metal tube blank as recited in the aforementioned Item 1 or 2, wherein the discharge opening is formed in an outer peripheral surface of a hollow rod.

[4] The method for drawing a metal tube blank as recited in any one of Items 1 to 3, wherein the lubricant is discharged toward a region of the inner surface of the tube blank positioned within a center angle of 30° at both sides in a circumferential direction from a highest position of the inner surface of the tube blank.

[5] The method for drawing a metal tube blank as recited in any one of Items 1 to 4, wherein the lubricant is discharged forwardly of the discharge opening.

[6] The method for drawing a metal tube blank as recited in any one of Items 1 to 5, wherein the lubricant is discharged from a nozzle provided on a periphery of the discharge opening.

[7] An apparatus for drawing a metal tube blank by passing the metal tube blank between a die for shaping an outer surface of the tube blank and a plug for shaping an inner surface of the tube blank, comprising:

a discharge opening configured to discharge lubricant, the discharge opening being opened in an outer peripheral surface of a hollow rod supporting the plug and provided only in a region of the tube blank higher than a center of the rod in an up-and-down direction; and

a discharge control device configured to intermittently discharge the lubricant and suspend the discharge of the lubricant during the drawing of the tube blank.

Effects of the Invention

In the invention recited in the aforementioned Item [1], the lubricant is discharged toward the upper region of the inner surface of the tube blank through the discharge opening of the rod to apply the lubricant to the portion of the inner surface of the tube blank including the highest position of the inner surface to thereby make the lubricant adhere to a portion of the inner surface of the tube blank lower than the lubricant applied position by the lubricant flowing down from the lubricant applied position. Thus, an excessive amount of lubricant which will accumulate in a lower region of the tube blank can be decreased. Further, by intermittently discharging the lubricant, an excessive supply amount of lubricant can be decreased as much as possible while giving a momentum of the discharge flow to reach the inner surface of the tube blank. Therefore, the required amount of lubricant can be adhered to the inner surface of the tube blank both in the circumferential direction of the tube blank and in the longitudinal direction of the tube blank and that an excessive amount of the lubricant can be decreased as much as possible.

According to the invention as recited in the aforementioned Item [2], by gradually increasing the discharge amount of the lubricant, possible shortage of lubricant in the upper region of the tube blank due to the processing heat generated by the drawing process can be prevented. In detail, the temperature of the lubricant is raised by the processing heat generated by the drawing process. As the temperature of the lubricant rises, the viscosity of the lubricant decreases. As the viscosity of the lubricant decreases, the amount of lubricant which will flow down increases and the amount of lubricant that adheres to the upper region decreases. However, gradually increasing the discharge amount of lubricant can prevent shortage of lubricant in the upper region.

According to the invention as recited in the aforementioned Item [3], since the rod can be used as a lubricant supplying path, the lubricant supplying structure can be simplified.

According to the invention as recited in the aforementioned Item [4], since the lubricant is applied to the highest position of the inner surface of the tube blank and the vicinity thereof where an amount of lubricant tends to become insufficient, shortage of lubricant in the region can be prevented assuredly.

According to the invention as recited in the aforementioned Item [5], lubricant can be discharged forwardly of the position of the discharge opening, shortening the distance from the lubricant supplied position to the bearing portion of the plug, which enables assured adhering of lubricant to a position of the bearing portion where lubricant tends to become insufficient.

According to the invention as recited in the aforementioned Item [6], since the nozzle is protruded from the outer circumferential surface of the rod, the discharge position of lubricant comes closer to the tube blank. Therefore, even in cases where the inner diameter of the tube blank is large with respect to the diameter of the rod and/or the discharge amount of lubricant is small, the lubricant can be assuredly adhered to the predetermined position. Furthermore, because the nozzle functions as a dam at the time of suspending the supply of lubricant, the lubricant is prevented from being flowed out through the discharge opening provided at a position other than the apex of the rod.

According to the invention as recited in the aforementioned Item [7], the drawing method as recited in Items [1] to [6] can be implemented. Since the discharge opening for lubricant is provided only at the upper region of the rod, when the supply of lubricant is suspended, the lubricant filled in the inner portion of the rod does not flow out, or even if the lubricant flows out, the flowed amount is slight. As a result, during the suspension of the supply of lubricant, the inner portion of the rod is filled with or almost filled with the lubricant. Therefore, after completion of drawing a single tube blank, even if the supply of lubricant is suspended between talking out the drawn tube from the device and setting a subsequent tube blank to the device, the inner portion of the rod is filled with or almost filled with lubricant. Therefore, when the supply of lubricant is resumed, lubricant can be discharged immediately or in a very short time through the discharge opening. For this reason, in continuously drawing a plurality of tube blanks, even in the case of the intermittent supply of lubricant in which the supply of lubricant is suspended when setting a subsequent tube blank, burning can be prevented by assuredly making lubricant adhere to an inner surface of each tube blank from the initiation of drawing each tube blank. Furthermore, since there is no need to wait for the recovery of the discharged amount of lubricant after resuming the supply of lubricant, processing can be performed efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view showing an example of a drawing apparatus for carrying out a drawing method of a metal tube according to the present invention.

FIG. 2 is a transverse cross-sectional view of a tube blank and a rod in a drawing device shown in FIG. 1.

FIG. 3 is a transverse cross-sectional view of another embodiment of a rod.

FIG. 4 is a transverse cross-sectional view of still another embodiment of a rod.

FIG. 5 is a transverse cross-sectional view of still yet another embodiment of a rod.

FIG. 6 is a longitudinal cross-sectional view of still yet another embodiment of a rod.

FIG. 7 is a longitudinal cross-sectional view of still yet another embodiment of the rod.

FIG. 8 shows graphs showing changes of a discharge amount of lubricant or an amount of lubricant adhered to an inner surface of a tube blank in a drawing method of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of a drawing apparatus for carrying out a drawing method for a metal tube according to the present invention. The drawing apparatus 1 is equipped with a drawing tool and a lubricant supplying portion for supplying lubricant to an outer surface and an inner surface of the tube blank 2.

The drawing tool includes a drawing die 10 and a plug 11. The drawing die 10 is provided with a die main body 13 fitted in a die case 12, and the die main body 13 has an approach portion 14 formed around a center die hole and a bearing portion 15 continued from the approach portion 14. The plug 11 is attached to a tip end of a rod 20 formed by a hollow tube and supported by the rod 20, and has an approach portion 16 and a bearing portion 17 continued from the approach portion 16. By drawing a tube blank 2 by passing through between the drawing die 10 and the plug 11, an outer surface of a drawn tube is formed or shaped by the approach portion 14 and the bearing portion 15 of the die main body 13 and an inner surface thereof is formed or shaped by the approach portion 16 and the bearing portion 17 of the plug 11. Thus, a drawn tube 3 is produced.

As a lubricant supplying portion for supplying lubricant to an outer surface of the tube blank 2, a nozzle 18 is arranged above and rearward of the drawing die 10. The lubricant L supplied from a tank (not illustrated) is discharged from the nozzle 18 toward the tube blank 2, and the lubricant L adhered to the upper portion of the tube blank 2 travels on the outer surface of the tube blank 2 to be supplied to the entire outer surface of the tube blank. The excessive lubricant L will flow downward. The tube blank 2 is introduced into the drawing tool with the lubricant L adhered to the outer surface of the tube blank 2.

As a lubricant supplying portion for supplying lubricant to an inner surface of a tube blank 2, a lubricant discharge opening 21 is formed in the rod 20. The rod 20 is a hollow tube and is utilized as a supplying passage for supplying lubricant L. By drilling the peripheral wall of the tube, the discharge opening 21 communicating with the supplying passage is formed. In this way, by forming the discharge opening 21 in the outer circumferential surface of the hollow rod 20, the rod 20 can be used as a lubricant supplying passage, and therefore the structure for supplying lubricant can be simplified. In this embodiment, a single discharge opening 21 is formed at the apex (i.e., the highest position in the up-and-down direction) of the rod 20 so as to face straight upward. The lubricant L introduced into the inner space of the rod 20 via the rear portion thereof from a tank (not illustrated) is discharged to the inner upper wall surface of the tube blank 2 to be applied and adhered thereto, and then travels on the wall surface and spreads in the peripheral direction. When the tube blank 2 is drawn while supplying lubricant L to the inner surface of the tube blank 2, the tube blank 2 is introduced into the drawing tool with the lubricant L adhered to the entire inner surface of the tube blank 2. Some lubricant L adhered to the tube blank 2 is carried out together with the drawn tube 3, and the remainder remains in the tube blank 2 to be carried to the rear portion of the tube blank 2. The switching between discharge of lubricant L and suspension of the discharge and the adjustment of the discharge amount of the lubricant L are controlled by the discharge control device 45.

In the drawing method of the present invention, the discharge direction, the apply position, and the discharge amount of the lubricant L discharged from the discharge opening 21 of the rod 20 to the inner surface of the tube blank 2 while drawing the tube blank 2 are specified as follows.

<Discharge Direction and Apply Position of Lubricant>

The lubricant L is discharged toward the upper region 40 of the inner surface of the tube blank 2 through the discharge opening 21, and adhered to a portion including the highest position P₁. The upper region 40 is defined as a region positioned higher than the center of the tube blank 2 in the up-and-down direction or in the vertical direction. In the cross-sectional view of the tube blank 2 and the rod 20 shown in FIG. 2, “H” denotes a horizontal plane passing through the center of the tube blank 2. The region positioned higher than the horizontal plane H is the upper region 40 of the inner surface of the tube blank 2 of the present invention, while the region positioned lower than the upper region 40 including the horizontal plane H is a lower region 41. “P₂” is the lowest position of the inner surface of the tube blank 2.

When lubricant L is discharged and adhered to a portion including the highest position P₁, the adhered lubricant L flows down along the wall surface to be naturally supplied to a portion lower than the portion to which the lubricant L was applied, and the lubricant L eventually accumulates at a portion including the lowest position P₂. Therefore, by discharging the lubricant L to the portion of the upper region 40 including the highest position P₁, the lubricant L is also supplied to a portion in the upper region 40 in which the lubricant L was not applied and the lower region 41. Thus, the lubricant L will be supplied to the entire inner circumference of the tube blank 2.

Excellent drawing can be achieved as long as the amount of lubricant L meets a required amount. An excessive amount of lubricant L will be either carried out together with the drawn tube 3 or sent to the rear of the tube blank 2. As the amount of lubricant L carried out together with the drawn tube 3 increases, a later cleaning process becomes more troublesome and the excess amount of the lubricant L remained in the tube blank 2 goes to waste. Therefore, as long as a required amount of lubricant L is adhered to the entire circumference of the inner surface of the tube blank 2, an excessive amount exceeding the required amount is preferably decreased as much as possible.

Also, under the circumstances in which the amount of lubricant L tends to become insufficient in the upper region 40 due to the flowing down of the lubricant L, if the adhered amount of lubricant L at the applied position of the upper region 40 meets a required amount, a required amount of lubricant L will be naturally supplied to the lower region 41. Therefore, in order to decrease an excessive amount of leftover lubricant in the lower region 41 as much as possible, the lubricant L is only discharged toward the upper region 40 and not discharged toward the lower region 41. The discharge direction of the lubricant L is defined by the center of the discharge flow, and as long as the center of the discharge flow goes toward the upper region 40 and the highest position P₁ is included in the lubricant apply position, the requirements of the present invention are met. Therefore, the present invention includes the case in which a part of the lubricant L discharged toward the upper region 40 is adhered to the lower region 41 due to diffusion of the discharge flow.

Further, among the upper region 40 of the tube blank 2, the highest position P₁ and the vicinity thereof tend to become insufficient in the amount of lubricant, and therefore it is preferable to discharge the lubricant L toward the region including the highest position P₁ and the vicinity thereof. Provided that the position of the inner surface of the tube blank 2 in the circumferential direction is represented by an angle α from the highest position P₁ with respect to the center of the tube blank 2, the preferable lubricant apply position 40 a can be represented by a region within a range of a center angle α on both circumferential sides from the highest position P₁ (see FIG. 2). In the present invention, the preferred lubricant apply position is a region within a range of an angle α=30° on both circumferential sides from the highest position P₁.

The discharge direction and the apply position of the lubricant L can be set by the position of the discharge opening 21. In this disclosure, the position of the discharge opening 21 in the circumference direction is defined by an angle θ from the apex of the rod with respect to the center of the rod 20. A discharge opening 21 is provided at a position of θ=0° in the rod 20 shown in FIG. 2, so the lubricant L is discharged straight upward, and because of diffusion of the discharge flow, the highest position P₁ and the vicinity thereof become a lubricant apply position. The apply range of the lubricant L differs depending on, in addition to the position of the discharge opening 21, the diffusion angle of the discharge flow, the inner diameter of the tube blank 2, and the distance between the discharge opening 21 and the inner surface of the tube blank 2, and therefore they are arbitrarily set so that the lubricant L can be applied to a predetermined position.

The position of the discharge opening is not limited as long as the lubricant L can be applied to the upper region 40 including the highest position P₁ because the discharged lubricant L is applied to the inner surface of the tube blank 2 in a spread manner and therefore, even if it is discharged from a position lower than the apex of the rod, it can be applied to the highest position P₁. Also, the number of discharge openings is not limited, and it can be configured to discharge lubricant L from a plurality of discharge openings. In the case of discharging lubricant L from a plurality of discharge openings, it is sufficient that the lubricant L discharged from at least one discharge opening is applied to a portion including the highest position P₁. FIG. 3 shows an example of a rod 22 in which two discharge openings 23 and 23 are provided at positions satisfying 0°<θ<90°, and the lubricant L can be applied to the highest position P₁ of the tube blank 2 from both directions due to the diffusion of the discharge flow of lubricant L. Further, in the case of sequentially drawing a plurality of tube blanks, the supply of lubricant is suspended in order to set a subsequent tube blank 2. In this case, in order to reduce the amount of lubricant L flowing out of the discharge opening during the suspension of the supply of lubricant L, it is preferable to provide a discharge opening 23 so that the angle θ falls within the range of 60° or less, more preferably within the range of 40° or less because of the following reasons. As the angle θ becomes larger, the position of the discharge opening 23 becomes lower, increasing the flow amount of the lubricant during the suspension of the supply of lubricant, which in turn deteriorates the responsiveness at the time of resuming the supply of lubricant. Further, lubricant L applied to the inner surface of the tube blank 2 would not flow to a portion higher than the lubricant applied position. Therefore, in cases where shortage of lubricant might occur at the highest portion P₁ of the tube blank 22 or the vicinity thereof when lubricant is discharged obliquely upward with the rod 22 shown in FIG. 3, such a problem of the shortage of lubricant can be easily solved by adding a discharge opening at the apex of the rod or the vicinity thereof. The rod 24 shown in FIG. 4 is an example in which three discharge openings are provided by adding a discharge opening 21 (arranged at the position of θ=0° shown in FIG. 2 to two discharge openings 23 and 23 (arranged at the position of 0°<θ<90° shown in FIG. 3.

Further, as shown in FIG. 5, it is also preferable to attach a nozzle 26 to the periphery of a discharge opening 21 formed in a peripheral wall of the rod 25 so as to protrude from the outer peripheral surface of the rod 25. Providing the nozzle 26 results in a closer discharge position of the lubricant with respect to the tube blank 2. Therefore, even in cases where the inner diameter of the tube blank 2 is large with respect to the diameter of the rod 25 and/or the discharge amount of lubricant is small, it becomes possible to assuredly make lubricant adhere to a predetermined position. Furthermore, the nozzle 26 functions as a dam during the suspension of the supply of lubricant, which prevents the lubricant from flowing out of the discharge opening provided at a position other than the position of θ=0°.

Also, in the present invention, the supply of lubricant is repeatedly suspended and resumed to intermittently discharge the lubricant during the drawing of a tube blank, but since the cycle of the supply of lubricant and the suspension of the supply of lubricant is short, the lubricant will not flow out of the discharge opening while the supply of lubricant is suspended. The suspension of the supply of lubricant for intermittently discharging the lubricant during the drawing process is different from the suspension of the supply of lubricant for setting a subsequent tube blank.

Further, it is preferable that the discharge opening is provided at a position closer to the bearing portion of the plug in a drawing direction. The lubricant L applied to the inner surface of the tube blank flows downward during which the tube blank 2 is moved from the position of the discharge opening 21 to the position of the bearing portion 17 of the plug 11, which tends to cause occurrence of shortage of lubricant at the highest position P₁ of the tube blank 2 and the vicinity thereof. To cope with the flow down of lubricant L, the position of the discharge opening 21 is arranged closer to the bearing portion 17 to thereby reduce the distance from the applied position of the lubricant L to the bearing portion 17, so that it becomes possible to assuredly make the lubricant L adhere to the upper region of the bearing portion 17 where shortage of lubricant L tends to occur and also it becomes possible to efficiently make the lubricant L adhere to the inner surface of the tube blank 2. From this point of view, it is preferable to provide the discharge opening 21 at a position within 20 cm or less, more preferably 10 cm or less, from the bearing portion 17. In the structure in which the tip end portion of the rod 20 is inserted into and secured to the plug 11 as shown in FIG. 1, it should be noted that the present invention covers the case in which the discharge opening is provided at a portion where the tip end portion of the rod 20 and the plug 11 are overlapped.

Furthermore, it is also preferable to discharge lubricant L from the discharge opening forwardly or toward the front side. As mentioned above, although the lubricant apply position can be arranged closer to the bearing portion 17 by providing the discharge opening 21 at a location near the bearing portion 17, the lubricant apply position can be arranged more closer to the bearing portion by discharging the lubricant L forwardly or toward the front side from the position where the discharge opening is provided. As a means for setting the discharge direction of the lubricant L, structures shown in FIGS. 6 and 7 can be exemplified. In the rod 27 shown in FIG. 6, the peripheral wall is drilled obliquely so that the discharge opening 28 faces forwardly or toward the front side. In the rod 29 shown in FIG. 7, the nozzle 30 is attached to the discharge opening 28 formed in the peripheral wall of the rod 29 so as to face forwardly or toward the front side.

<Apply Amount of Lubricant>

A tube blank 2 which is being drawn raises in temperature toward the rear portion due to the processing heat. The lubricant L adhered to the tube blank 2 or the lubricant L passing through the inside of the rod 20 rises in temperature toward the rear portion, resulting in an easy flow down of the lubricant due to the decreased viscosity. The amount of lubricant that flows down while the lubricant L adhered to the applied position reaches the plug 11 increases toward the rear portion, and therefore if a constant amount of the lubricant L is discharged in the lengthwise direction of the tube blank 2, the adhered amount of the lubricant L at the time when the adhered lubricant reaches the plug 11 gradually decreases in the upper region 40 and gradually increases in the lower region 41. To cope with this situation, in the present invention, by changing the discharge amount of the lubricant L so that the amount of applied lubricant L gradually increases, a required amount of the lubricant L can be secured at the upper region 40 of the rear portion of the tube blank 2 to prevent the possible occurrence of shortage of lubricant, and the amount of the lubricant which excessively accumulates in the lower region 41 can be decreased as much as possible. “The amount of applied lubricant L gradually increases” means that, in an intermittent discharge of lubricant during a process of drawing a single tube blank, the discharge amount of the lubricant at the n^(th) intermittent discharge of lubricant is increased as compared with the lubricant discharge amount of the (n−1)^(th) intermittent discharge of lubricant. Changing the discharge amount can be performed by adjusting the discharge amount per unit time or by adjusting the discharge time.

The lubricant L is intermittently applied to the inner surface of the tube blank by intermittently discharging the lubricant. “Intermittently discharging” means that the discharge of lubricant and the suspension of the discharge of lubricant are alternately repeated. In order for the lubricant L discharged upward to reach the inner surface of the tube blank 2, it is required to give the discharge flow burst of momentum. In order to give the discharge flow burst of momentum, it becomes necessary that the discharge amount of lubricant per unit time should be set to be a certain amount or more. However, if the lubricant is continuously discharged while keeping the discharge amount of the lubricant, the amount of applied lubricant becomes excessive, resulting in an increased amount of lubricant to be carried out together with the drawn tube 3 and an increased amount of lubricant remained in the tube blank 2. Therefore, in the present invention, in order to decrease the excess supply amount of lubricant as much as possible while securing the momentum of the discharge flow of the lubricant L, the lubricant L is intermittently applied to the inner surface of the tube blank 2 by intermittently discharging the lubricant.

In this way, in the present invention, when using lubricant having a relationship between the temperature and the viscosity in which the viscosity decreases as the temperature rises, the lubricant L is intermittently discharged so that the amount of lubricant applied to the inner surface of the tube blank 2 gradually increases.

<Drawing Tests>

Using the rod 20 shown in FIG. 2 in the drawing apparatus 1, drawing tests were performed while changing conditions of discharging lubricant to the inner surface of the tube blank 2. The lubricant supply to the outer surface of the tube blank 2 was performed in the same manner through the tests.

In the drawing apparatus 1, the die main body 13 of the drawing die 10 had an approach portion 14 having an approach angle of 15° and a bearing portion 15 having a bearing length of 15 mm. The approach angle of the approach portion 16 of the plug 11 was 7°, and the bearing length of the bearing portion 17 was 2 mm.

The rod 20 was provided with a single discharge opening 21 at the position of θ=0°, the discharge direction of the lubricant L was set to be straight upward, and the lubricant applied position was set to be the highest position or the vicinity thereof on the inner surface of the tube blank 2. The discharge opening 21 was provided rearward of the bearing portion 17 of the plug 11 by 10 cm. As the lubricant L for the inner and outer surfaces of the tube blank 2, Strol ES150 (viscosity: 1.4×10⁻⁴ m²/s) made by Kyoei Yuka Kabushiki Kaisha was used.

EXAMPLES

As shown by the thick solid lines in the upper graph in FIG. 8, the lubricant L was intermittently discharged from initiation of a drawing process at constant intervals, and the discharge amount of the lubricant per discharge was gradually increased.

COMPARATIVE EXAMPLE

As shown by the thin solid lines in the upper graph in FIG. 8, setting the discharge amount of lubricant per discharge to be constant, the lubricant was intermittently discharged at the same intervals as those in Example.

The middle graph in FIG. 8 shows the changes in the adhered amount of the lubricant L at the highest position P₁ in the upper region 40, and the lower graph shows the changes in the adhered amount of the lubricant L at the lowest position P₂ in the lower region 41. In the graphs of FIG. 8 showing the changes in the adhered amount of lubricant, the thick solid lines show the Example of the present invention, and the thin solid lines show the Comparative Example. Also, the dash lines show a required amount of lubricant L, indicating that an amount less than the required amount will cause shortage of lubricant. Also, FIG. 8 shows discharges of lubricant in Example and Comparative Example by shifting them by a ½ cycle. It should be understood that this was done to make it easier to see the difference for the convenience of an easy explanation, and does not accurately show the timing of discharge from the initiation of the drawing process.

In Example and Comparative Example, when the lubricant L was discharged to the upper region 40 of the inner surface of the tube blank 2, the adhered amount of the lubricant L at the highest position P₁ of the upper region became maximum immediately after the discharge, the adhered amount of the lubricant L gradually decreased due to the carrying out of the lubricant by the drawn tube 3 and flowing down of the lubricant, and the increase and decrease in the adhered amount of the lubricant L were repeated due to the intermittent discharges. Although the amount of lubricant flowing down was gradually increased due to the processing heat, because each discharge amount of lubricant per discharge was gradually increased in Example, the minimum adhered amount did not fall below the required amount. On the other hand, in Comparative Example, since the amount of lubricant discharged per discharge was constant, the amount of adhered lubricant fell below the required amount at the rear portion when the amount of lubricant flowing down was increased gradually. In a constant discharge of lubricant like in Comparative Example, if the lubricant discharge amount is set so that the required amount can be secured even at the rear portion of the tube blank, the excess amount of lubricant in the front portion increases, which causes inconveniences such as an increase in the carried out amount of lubricant to the drawn tube 3 and the consumption amount of the lubricant L. In other words, if the lubricant discharge amount is set so that the required amount can be secured at the rear portion of the tube blank, the amount of lubricant at the front portion of the tube blank becomes far excessive exceeding the required amount of lubricant.

On the other hand, at the lowest position P₂ of the lower region 41, since the lubricant L is supplied by the flowing down of the lubricant L from above, the adhered amount of lubricant L becomes maximum and minimum with the timing being off from the initiation of discharge of lubricant. At the lowest position P₂, the lubricant accumulates with the exception of the amount carried out together with the drawn tube 3, and since the adhered amount of lubricant increases toward the rear portion of the tube blank while repeating increase and decrease in the amount of lubricant, shortage of lubricant does not occur at the rear portion of the tube blank. Such an increase and decrease pattern is common in Example and Comparative Example. Also, as long as an amount of lubricant L which does not fall below the required amount is discharged when the adhered amount of lubricant becomes minimum at the highest position P₁, the amount of lubricant at the lowest position P₂ does not fall below the required amount.

Further, since the lubricant L flows down to be adhered to portions of the tube blank other than the lubricant applied position, as long as the adhered amount of the lubricant L at the highest position P₁ shown in the figure meets a required amount and an amount of lubricant L meeting the required amount is accumulated at the lowest position P₂, an amount of the lubricant L meeting the required amount is adhered to portions of the tube blank in between the highest position P₁ and the lowest position P₂. Therefore, in Example of the present invention, an amount of lubricant L meeting the required amount was adhered to the portions between the highest position P₁ and the lowest position P₂ not illustrated in the graphs of FIG. 8, and the required amount of lubricant L can be adhered to the entirety of the tube blank in the circumferential direction.

In this manner, by intermittently discharging the lubricant L while changing the discharge amount of the lubricant L so that the amount of lubricant applied to the inner surface of the tube blank 2 gradually increases, the lubricant L can be applied to the tube blank both in the circumferential direction and in the lengthwise direction of the tube blank 2 so as not to cause shortage of the lubricant, which prevents occurring of burning. Also, since the lubricant L is discharged from the discharge opening 21 of the rod 20 supporting the plug 11, a predetermined amount of lubricant L can be adhered regardless of the length of the tube blank 2, and no core for spreading the lubricant is required.

The discharge amount and the increase amount of the lubricant are arbitrarily set depending on, e.g., the viscosity of the lubricant, the length and the diameter of the tube blank, and the processing heat to be generated during the drawing process.

It should be noted that the method for gradually increasing the discharge amount of lubricant is not limited to the aforementioned example in which the discharge amount of lubricant per discharge is increased. The discharge amount of lubricant can be gradually increased by increasing the discharge time for each discharge or by shortening the discharge interval. The gradual increase in the discharge amount of the lubricant L can be performed by combining the aforementioned methods. The discharge conditions are set by the discharge control apparatus 45.

When the tube blank 2 is set to the drawing apparatus 1, the lubricant L cannot be discharged to the forward portion of the tube blank 2 between the plug 11 and the discharge opening 21. Further, as to the portion of the tube blank 2 positioned rearward of the discharge opening 21 and downward of the lubricant applied position, the lubricant L will not be applied until the lubricant flows to the portion from the lubricant applied portion. In order to cope with such shortage of lubricant on a drawing initiation portion of the tube blank, the lubricant L can be applied in advance to the forward portion of the tube blank 2 or the lubricant L can be applied to the plug 11.

In the case of sequentially drawing a plurality of tube blanks with the drawing apparatus 1, the drawing process and the lubricant supply to the inner surface of the tube blank are performed by repeating the following steps:

(i) a step of drawing the tube blank 2 while intermittently discharging lubricant L to the portion of the inner surface of the tube blank 2 including the highest position P₁ from the discharge opening 21 by supplying the lubricant L to the rod 20 so that the discharge amount of the lubricant L gradually increases;

(ii) a step of suspending the supply of the lubricant L after completion of the drawing process of a single tube blank 2;

(iii) a step of taking out the drawn tube from the drawing apparatus 1 and setting a subsequent tube blank to the drawing apparatus;

(iv) a step of resuming the supply of lubricant L;

(v) a step of supplying lubricant L until a discharge amount of lubricant becomes stable;

(vi) a step of returning to Step (i).

Since the lubricant L is supplied during the drawing step (i), the inner side of the rod 20 is filled with lubricant L. When the supply of lubricant L is suspended at Step (ii), the lubricant L in the rod 20 flows out until the liquid level goes down to the height of the discharge opening 21 during exchanging tube blanks at Step (iii). For example, in the case of the rod 20 shown in FIGS. 1 and 2, since the discharge opening 21 is formed at the apex of the rod 20, the lubricant L will not flow out. However, in the case of the rod 22 shown in FIG. 3, since the discharge opening 23 of the rod is formed at a position lower than the apex of the rod 20, the lubricant L flows out until the liquid level goes down to the height of the discharge opening 23. Even if the supply of lubricant L is resumed at Step (iv), lubricant will not be discharged until the amount of lubricant flowed out is compensated. When the inside of the rod 22 is filled with lubricant L via Step (v), discharge of lubricant L will be resumed. After establishing the stable discharge of lubricant, the step proceeds to Step (vi). Step (v) is a waiting time for waiting for the recovery of the amount of lubricant flowed out by compensating the amount of lubricant flowed out. As the amount of lubricant flowed out becomes smaller, the waiting time can be shortened and the lubricant discharge responsiveness improves. If drawing of the subsequent tube blank 2 is executed by omitting Step (v), lubricant shortage occurs at the drawing initiation portion of the tube blank.

In the present invention, since the discharge opening is provided only at the region higher than the center of the rod in the up-and-down direction or in the vertical direction, the amount of lubricant flowed out during the suspension of the supply of lubricant is small. Further, the lubricant can be assuredly supplied to the inner surface of the tube blank from the initiation of the drawing and the aforementioned waiting time can be reduced as much as possible to thereby shorten the time required for continuously drawing a plurality of tube blanks.

Oil-based lubricant was used for the drawing tests, but the present invention is not limited to the case in which oil-based lubricant is used as lubricant. In the present invention, the aforementioned effects can be achieved by water-based lubricant.

The drawing method of a metal tube according to the present invention is not limited by a type of metal, and can be widely applied to a method for drawing a tube blank of, e.g., aluminum, iron, copper or alloys thereof. Remarkable effects can be exerted when drawing a long tube blank, and therefore the drawing method of the present invention is suitable for manufacturing an aluminum tube for a photoconductive drum substrate. In manufacturing an aluminum tube for a photoconductive drum substrate, there is a tendency to use a long tube blank to manufacture a number of product tubes by a single drawing process. Therefore, by applying the drawing method of the present invention, high quality aluminum tubes small in deflection can be manufactured efficiently. Furthermore, even in the case of performing a continuous drawing of two or more passes in which a tube blank is drawn twice or more for the purpose of enhancing the dimensional precision, it is not required to perform any operation for supplying lubricant between passes, resulting in quick continuous drawing. Furthermore, as a material of an aluminum tube for use in photoconductive drum substrates, Al—Mn series alloy, Al—Mg series alloy, Al—Mg—Si series alloy, and pure aluminum can be exemplified.

This application claims priority to Japanese Patent Application No. 2010-63464 filed on Mar. 19, 2010, and the entire disclosure of which is incorporated herein by reference in its entirety.

It should be understood that the terms and expressions used herein are used for explanation and have no intention to be used to construe in a limited manner, do not eliminate any equivalents of features shown and mentioned herein, and allow various modifications falling within the claimed scope of the present invention.

INDUSTRIAL APPLICABILITY

According to the drawing method for a metal tube of the present invention, lubricant can be assuredly and effectively applied to an inner surface of a tube blank when continuously drawing a plurality of tube blanks, and therefore the method is suited for mass production of aluminum tubes for photoconductive drum substrates.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 . . . drawing apparatus -   2 . . . tube blank (raw tube) -   3 . . . drawn tube -   10 . . . drawing die -   11 . . . plug -   20, 22, 24, 25, 27, 29 . . . rod -   21, 23, 28 . . . discharge opening -   26, 30 . . . nozzle -   40 . . . upper region -   45 . . . discharge control apparatus -   L . . . lubricant -   P₁ . . . highest position -   α . . . angle indicating the preferred region of a lubricant apply     position 

1. A method for drawing a metal tube blank, while drawing the metal tube blank between a die for shaping an outer surface of the tube blank and a plug for shaping an inner surface of the tube blank, intermittently discharging lubricant through a discharge opening formed in a rod supporting the plug toward an upper region of the tube blank positioned higher than a center of the tube blank in an up-and-down direction to apply the lubricant to a portion of the inner surface of the tube blank including the highest position of the inner surface of the tube blank.
 2. The method for drawing a metal tube blank as recited in claim 1, wherein the lubricant is discharged intermittently in a manner such that a discharge amount of the lubricant is gradually increased.
 3. The method for drawing a metal tube blank as recited in claim 1, wherein the discharge opening is formed in an outer peripheral surface of a hollow rod.
 4. The method for drawing a metal tube blank as recited in claim 1, wherein the lubricant is discharged toward a region of the inner surface of the tube blank positioned within a center angle of 30° at both sides in a circumferential direction from a highest position of the inner surface of the tube blank.
 5. The method for drawing a metal tube blank as recited in claim 1, wherein the lubricant is discharged forwardly of the discharge opening.
 6. The method for drawing a metal tube blank as recited in claim 1, wherein the lubricant is discharged from a nozzle provided on a periphery of the discharge opening.
 7. An apparatus for drawing a metal tube blank by passing the metal tube blank between a die for shaping an outer surface of the tube blank and a plug for shaping an inner surface of the tube blank, comprising: a discharge opening configured to discharge lubricant, the discharge opening being opened in an outer peripheral surface of a hollow rod supporting the plug and provided only in a region of the tube blank higher than a center of the rod in an up-and-down direction; and a discharge control device configured to intermittently discharge the lubricant and suspend the discharge of the lubricant during the drawing of the tube blank. 